A frequency comb is a spectrum consisting of a discrete set of equally spaced frequency elements. Frequency comb generation generally involves the combination of an optical laser source with a nonlinear process. Frequency combs can be generated by a number of mechanisms, including amplitude modulation in continuous wave lasers or stabilization of pulse trains generated by semiconductor, mode locked lasers. Four-wave mixing can be used in microresonators and quantum cascade lasers to produce frequency combs. However, frequency comb generation using existing terahertz (frequency range 0.1-10 THz) quantum cascade laser systems requires cryogenic cooling to operate and has limited bandwidth for comb generation. Optical frequency combs provide a useful tool with applications in numerous areas, including spectroscopy, metrology, sensing, ranging, and distance measurement.
While specific embodiments are shown by way of example in the drawings and the accompanying detailed description, various other modifications and alternative forms are possible. It should be understood that the drawings and detailed description are not intended to be limiting.